1. Field of the Invention
The present invention relates to a device and a method of exchanging a tool between a tool exchange holding device and a spindle which is capable of approaching and moving way from the tool exchange holding device. More particularly this invention relates to a device which retrieves tools from a tool holding device while the spindle continues to work and prior to exchanging of the tool in a spindle.
2. Description of Related Art
Various mechanisms have been designed for loading and unloading tools into the spindle of printed wire board drilling and routing machines and other automatic machine tools. These are typified by U.S. Pat. No. 5,111,573 to ITO, U.S. Pat. No. 5,407,416 to OTTONE et. al., and U.S. Pat. No. 5,068,958 to KOSMOWSKI. Most of these systems store the tools in a magazine or a tool holder which is serviced from a tool changer mounted on the work table of the machine. The result of mounting the tool changer on the machine work table is to increase the amount of time required to change tools due to the movement of the work table to position the changer under the spindle, as well as affecting the speed at which the table can be positioned due to the extra weight of the tool changer mechanism. This occurs because the tool change process cannot begin to take place until the machine stops working. A typical tool change sequence is for the work table with tool changer to first move the work table to position the tool changer under the spindle, the tool is removed from the spindle and the work table moves to position the tool changer to the appropriate position under a magazine to return the tool to the magazine. Then the tool changer is positioned to extract the next tool from the magazine, remove it and then move back under the spindle at which time the tool is inserted into the spindle.
A similar situation exists with the pressure foot insert which are disclosed in U.S. Pat. No. 5,249,348 to Hall which is used to hold stacked printed wire boards for example, down against the machine work table during machining. Typically these inserts are mounted in separate holders which are also serviced by a changer mounted on the machine work table. Again the result is similar to that experienced with the tool changers, mounted in similar fashion, namely the time to change the insert is increased due to the fact that the changer is attached to the machine work table and the work table must be moved to position the tool changer to a tool change position accessible by the spindle.
Current tool changer designs reduce machine productivity because during the tool change process work is not being done. Since as much as 30 percent of the time spent drilling printed wire boards, for example, may be consumed by changing tools, a more time efficient means is very desirable.
In addition, where tools do not have collars, it is uncertain how much of the tool projects from the end of the spindle when loaded. This happens because the drill may have been resharpened and is shorter than when new or it may not have been inserted into the tool storage cassette the same distance as every other tool in the cassette. Thus, when the tool change mechanism grips a tool without a collar, it does so in an unspecified location which affects the distance the tool will ultimately project from the spindle.
Consequently, a coarse axial adjustment of the tool normally must be first made so that the location of the tool tip is approximately known. Typically, this is done after the tool is inserted into the collet of the spindle by a sequence of operations which entail opening and closing the collet of the spindle and transfer mechanism collets or grippers and a repositioning of the spindle in the axial direction. Such a system is described in U.S. Pat. No. 5,068,958. After the coarse adjustment is made, the spindle is positioned over a gauge which measures the location of the tool tip precisely and enters an offset value or correction factor into the computer to compensate for different tool tip distances. The coarse adjustment is time consuming and produces unreliability due to the wear and tear on the collet of the spindle and transfer collet or gripper mechanisms occasioned by the repeated opening and closing thereof. Total tool change time is increased as a result.